1. Field of the Invention
The present invention relates to a switching power supply device including a switching regulator such as a DC/DC converter.
2. Description of the Related Art
A switching power supply device including a switching regulator such as a DC/DC converter has prevailed as a power supply device for, for example, an image forming apparatus. In such a power supply device, a large-capacity capacitor is required to attain slow voltage and current changes with respect to load variations. Japanese Patent Laid-Open No. 2000-023355 has proposed means for suppressing output voltage variations based on a notice signal that gives notice of an abrupt change in the impedance of a load.
A switching regulator generally includes an overload protection circuit. However, depending on the arrangement of the overload protection circuit, the characteristics (drooping characteristics) of an output voltage with respect to an output current of the switching regulator unwantedly change to [\(backslash)] type characteristics. According to FIG. 4A, when an output current Iout exceeds Ia as a drooping start point, an output voltage Vout begins to droop. When the output current Iout reaches Ib as a load short point, the output voltage Vout becomes zero. In a switching power supply device having such [\(backslash)] type drooping characteristics, for example, when short-circuiting of a load has occurred, a current having a large peak value unwantedly flows through a switching element and rectifying element. This results in low reliability and depletion of the switching element and rectifying element.